The invention relates to hot air generators intended to be mounted in an open fireplace and essentially constituted by a shallow closed conduit comprising on the ground a horizontal part forming a hearth and chamber for pre-heating of the air and, on the backwall of the fireplace, a vertical part in which the air is slowed down by baffles and achieves its final temperature.
More precisely, the invention relates to hot air generators of the type set out above in which one of the faces of the shallow conduit is constituted by plates of cast iron assembled together. The cast iron has remarkable qualities in this situation, but also has the inconvenience of the difficulty of moulding complex forms without use of a core, and thus in practice one cannot consider the direct moulding by pouring of the portions of the closed shallow conduit. Also, in the prior art, the second face of the shallow conduit is constituted by a wall of masonry. As a result, this type of hot air generator cannot be installed in a fireplace which has already been constructed. Furthermore, this solution does not give perfect airtightness and thermal insulation.